Heat fluxes by the transient phenomena toward the first walls are investigated in a toroidal plasma device, called Korea Superconducting Tokamak Advanced Research (KSTAR) device, and a linear device called Divertor Plasma Simulator-2 (DiPS-2) by using triple electric probes installed on the walls of both KSTAR and DiPS-2.
Specific Type I ELMing H-mode discharges have been performed with a lower single magnetic geometry, where the outboard separatrix position is slowly (~7s) scanned over a radial distance of 7 cm, reducing the wall probe–separatrix distance to a minimum of ~9 cm, and allowing the ELM filament heat loss to the wall to be analyzed as a function of radial propagation distance. A fast reciprocating probe (FRP) head is separately held at fixed position toroidally close and 4.7 cm radially in front of the wall probe. This FRP monitors the ELM ion fluxes, allowing an average filament radial propagation speed, found to be independent of plasma radial position, of 80 – 100 ms-1 to be extracted. Radial dependence of the peak filament wall parallel heat flux is observed to be exponential, with the decay length of λ_(q,ELM) ~ 23 ± 4 mm and with the heat flux of q_(∥,ELM) = 0.05 MWm-2 at the wall, corresponding to q_∥ ~ 7.5 MWm-2 at the second separatrix. Along with the measured radial propagation speed and the calculated radial profile of the magnetic connection lengths across the SOL, these data could be utilized to analyze filament energy loss model for the future machines
In DiPS-2, ELM phenomena have been simulated by a magnetic modulation. Transient heat and particle fluxes on the wall have been compared with those of KSTAR device. Magnetic modulation lead to periodic particle and energy release toward the wall, which seems to be similar to ELM phenomena of toroidal devices, in terms of energy loss rate and frequency. The energy loss rate due to transient heat flux in DiPS-2 (0.75 %), is found to be comparable to that of KSTAR (0.5 %).